More than a quarter century ago, spark-ignition engines tended to have only one intake valve. To improve breathing and, thus, peak power obtainable from a given displacement engine, two intake valves became common in production engines. Two intake valves, though, have been found to give less mixture motion at low-torque conditions than a single intake valve causing a detriment to idle quality. If the cross-sectional area of the port is reduced at low-torque conditions, the velocity of the flow past such reduced area section is increased. Valves placed in ducts in the intake manifold can be maintained open at high-torque operating conditions, but moved to a blocking position at low-torque operating conditions. Additionally, the contours of the valves are carefully designed to encourage flow characteristic leading to tumble and/or swirl.
Charge motion control valves (CMCVs), such as that shown in commonly-assigned U.S. Pat. No. 8,056,534, are provided to block secondary intake ducts of an intake system in some engines. The CMCVs in U.S. Pat. No. 8,056,534 use a butterfly valve similar to a throttle valve used for controlling the quantity of air delivered to the engine. The actuator shaft of the CMCV passes through the center of the intake runner as well as through the center of the intake runners of the primary intake ducts. The CMCV shafts running through the center of the secondary intake runners interacts with flow at high-torque conditions causing a pressure drop and interfering with the fluid mechanics. Even more problematic is when the shaft passes through the primary ducts as well thereby negatively impacting flow in those ducts as well.
To overcome this problem, the butterfly valve has been replaced with a flapper valve that is connected to a shaft that passes through one edge of the duct. It has been found that some flow passes through the dud behind the flapper valve, i.e., a gap that is between the CMCV shaft and the edge of the duct proximate the CMCV shaft. Such a gap allows flow when the CMCV is intended to be closed thereby defeating some of the benefit of the CMCV and leading to undesirable effects on the fluid mechanics. Even when the CMCV is open, the flow through the gap negatively impacts the fluid mechanics.
In one prior art seal disclosed in WO2013/137349 A1, a centrally-located shaft has seals applied to tips of the butterfly valve. Such seals applied to the moving portion of the valve has a substantial effect only when the valve is closed or nearly closed. Such a seal does not solve the problem with sealing the undesired flow path when the valve is open. Furthermore, it would not solve the problem of flow behind the flapper valve in any valve position.